// @flow
// function sum(a: number, b: number) {
//   return a + b
// }
// sum(100, 100)
// sum(100, '100')

/**
 * @flow
 */
function square(n) {
  return n * n
}
square(100)

let num: number = 100

function fn (): number {
  return 100
}

const a: 'foo' = 'foo'

const gender: ?number = null

const element: HTMLElement | null =  document.getElementById('1')